Basic Electricals - Section 1
Electric Voltage, Current and Resistance
Voltage, Current and Resistance are the three most basic parameters which form the foundation of electrical engineering. They describe how electrical energy is made available, how electric charge moves through a circuit, and how a material or component opposes that movement. Understanding their relationship is essential before progressing to more advanced subjects such as circuit analysis, power systems, electrical machines, protection, control systems, electronics, and power transmission.
Voltage — The Driving Force: Voltage is the difference in electric potential between two points. It provides the electrical "driving force" that can cause charge to move through a conducting path.
Current — The Flow of Electric Charge: Electric current represents the rate at which electric charge moves through a circuit. In a metallic conductor, current is associated with the movement of free electrons. In practical electrical systems, however, we normally describe current using the conventional direction of positive charge flow.
Resistance — Opposition to Current: Resistance describes the opposition that a material or component presents to the flow of electric current.
The relationship between them can be viewed as:
Voltage → drives current
Resistance → opposes current
Current → results from their interaction
With the above introduction, we have familiarized with the basic and major parameters of electrical system. Now, let us dig deep into each of these parameters and how they work.
Q1. What is Electric Charge?
A1. Electric charge is a physical property of matter that causes it to experience a force when placed in an electromagnetic field. Electric charge can be positive or negative. Like charges (i.e. two positives or two negatives) repel each other and unlike charges (i.e. one positive and one negative) attract each other.
Symbol: q or Q
Unit: coulomb (symbol: C) in SI units
Charge of an electron, e = 1.6 x 10-19 C.
Q2. What is Electron Drift Velocity?
A2. Drift velocity is the average velocity that free electrons attain in a conductor when an external electric field is applied. In a conductor, free electrons have random thermal motion. When an electric field is applied, they acquire a small net drift velocity.
Symbol: vd
Unit: m/s in SI units
Change is electric charge is described as – If n numbers of electrons of charge e, pass through a conductor of cross-section A with a drift velocity vd, then the change in electric charge is given by
dq = n.A.e.vd.dt
Where,
n= number of free electrons per m³
A= conductor cross-sectional area in m²
e= electronic charge in C
vd= drift velocity in m/s